Police are baffled as to how the man, believed to be a 37-year-old from Port Kembla near Wolllongong, came to be in Cowra and in the Lachlan River.

Police were called to Edgell Park in Cowra about 7am on Sunday morning after a report of a man laying on a river bank in the Lachlan.

"He was unresponsive," Inspector Adam Beard of Cowra Police said on Monday.

Inspector Beard said other emergency services also responded to the call, including Ambulance NSW and the Cowra Fire Brigade.

"Police entered the river and waded across to the sandbank, he was carried from the river to the riverbank where he was met by ambulance officers," Insp Beard said.

"His medical condition was very poor, he could not communicate with emergency services, possibly suffering from hypothermia."

The retrieval of the man was a combined effort by Cowra's emergency services with NSW Fire and Rescue also attending to lift him up the steep river bank onto a waiting ambulance.

Inspector Beard said the man was then flown from Cowra by air to Sydney's Westmead Hospital.

His condition is currently listed as serious but is improving, Inspector Beard said.

At the time he was located he was wearing just a pair of track suit pants.

Police are piecing together the man's movements through Saturday night but at this stage have been unable to establish how or why he came to be in the river.

Members of the public with information should contact Cowra Police on 6341 5099.